The present invention relates to techniques for producing fused proteins useful as immunogens for therapeutic and preventive vaccines and techniques for bioactive fused protein useful for treatment of various diseases by expressing genes for fused proteins of heat-labile enterotoxin B subunit (LTB) and a protein heterologous to heat-labile enterotoxin (LT), using recombinant techniques.
Surfactants have been used for enhancing absorption of foreign or bioactive substances (proteins) through nasal mucosa tissues, and choleratoxin has been studied for the purpose of immunization with foreign antigens through nasal mucosa tissues. However, it has been desired to develop a protein which enhances the absorption of foreign or bioactive sustances through nasal mucosa tissues and which is suitable for the immunization through nasal mucosa tissues.
With the object of preparing an antigen suitable for the absorption and immunization of a foreign or bioactive protein through nasal mucosa tissues by targetting the foreign or bioactive protein topically, the present inventors have conducted investigations. As a result, the present inventors have discovered that fused protein obtained by combining LTB with a heterologous protein by genetic engineering techniques can attain this object.